Open the spare wheel compartment and remove spare wheel and any other accumulated junk.
Open the boot lid and remove the rubber floor mat.
You will note the plywood floor is in three sections.
Remove the ten machine screws which secure the CENTRE section of the boot floor to the body frame.
Remove the ten cup washers to which the machine screws tighten.
With the palm of your hand, gently tap the underside of the centre floor section and lift it out.
Vacuum out all dust and other detritus which has accumulated in the spare wheel compartment.
Remove the electric wire feed to the tank unit.
Using a proprietary cleaner, such as "Hyperclean", thoroughly clean the top of the unit and an area 3" – 4" around it to prevent ingress of dirt to the tank.
Remove the three set screws which secure the tank unit to the tank.
GENTLY wiggle the tank unit to break the gasket seal and withdraw the unit from the tank.
The unit is of the geared type, the cork float having a gear wheel attached to the end of the actuating arm, which meshes with a similar gear which revolves the contact on the circular rheostat, thus varying the current sent to the gauge and thus showing the contents of the tank
The cork float has nothing to go wrong with it, apart from maybe falling out of its clamp.
The common fault with these units is seizure of the gears and shafts.
If the unit is seized, lubricate all moving parts on the shafts with good quality light oil (e.g. Three in One) and leave for about an hour.
After such time, GENTLY wiggle the float up and down until the spindles on the shaft free off and full movement of the float is obtained. Re – lubricate as required during this process. DO NOT FORCE THE FLOAT ACTUATING ARM – just wiggle gently until the spindles free off.
To check the rheostat, connect one wire of an AVO meter to the electrical terminal on the unit and one to the tank unit body. If there is no voltage, then the rheostat has either a break in the windings, or the wiper from the float actuating arm has snapped/bent resulting in no contact on the rheostat.
There are specialist firms who will rewind/repair these items.
Replacement of the unit is the reverse of dismantling, but do ensure the gasket is in good condition. If in doubt, replace/remanufacture.